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<FONT color="green">001</FONT>    /*<a name="line.1"></a>
<FONT color="green">002</FONT>     * Licensed to the Apache Software Foundation (ASF) under one or more<a name="line.2"></a>
<FONT color="green">003</FONT>     * contributor license agreements.  See the NOTICE file distributed with<a name="line.3"></a>
<FONT color="green">004</FONT>     * this work for additional information regarding copyright ownership.<a name="line.4"></a>
<FONT color="green">005</FONT>     * The ASF licenses this file to You under the Apache License, Version 2.0<a name="line.5"></a>
<FONT color="green">006</FONT>     * (the "License"); you may not use this file except in compliance with<a name="line.6"></a>
<FONT color="green">007</FONT>     * the License.  You may obtain a copy of the License at<a name="line.7"></a>
<FONT color="green">008</FONT>     *<a name="line.8"></a>
<FONT color="green">009</FONT>     *      http://www.apache.org/licenses/LICENSE-2.0<a name="line.9"></a>
<FONT color="green">010</FONT>     *<a name="line.10"></a>
<FONT color="green">011</FONT>     * Unless required by applicable law or agreed to in writing, software<a name="line.11"></a>
<FONT color="green">012</FONT>     * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.12"></a>
<FONT color="green">013</FONT>     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.13"></a>
<FONT color="green">014</FONT>     * See the License for the specific language governing permissions and<a name="line.14"></a>
<FONT color="green">015</FONT>     * limitations under the License.<a name="line.15"></a>
<FONT color="green">016</FONT>     */<a name="line.16"></a>
<FONT color="green">017</FONT>    <a name="line.17"></a>
<FONT color="green">018</FONT>    package org.apache.commons.math3.ode;<a name="line.18"></a>
<FONT color="green">019</FONT>    <a name="line.19"></a>
<FONT color="green">020</FONT>    <a name="line.20"></a>
<FONT color="green">021</FONT>    /** This class converts second order differential equations to first<a name="line.21"></a>
<FONT color="green">022</FONT>     * order ones.<a name="line.22"></a>
<FONT color="green">023</FONT>     *<a name="line.23"></a>
<FONT color="green">024</FONT>     * &lt;p&gt;This class is a wrapper around a {@link<a name="line.24"></a>
<FONT color="green">025</FONT>     * SecondOrderDifferentialEquations} which allow to use a {@link<a name="line.25"></a>
<FONT color="green">026</FONT>     * FirstOrderIntegrator} to integrate it.&lt;/p&gt;<a name="line.26"></a>
<FONT color="green">027</FONT>     *<a name="line.27"></a>
<FONT color="green">028</FONT>     * &lt;p&gt;The transformation is done by changing the n dimension state<a name="line.28"></a>
<FONT color="green">029</FONT>     * vector to a 2n dimension vector, where the first n components are<a name="line.29"></a>
<FONT color="green">030</FONT>     * the initial state variables and the n last components are their<a name="line.30"></a>
<FONT color="green">031</FONT>     * first time derivative. The first time derivative of this state<a name="line.31"></a>
<FONT color="green">032</FONT>     * vector then really contains both the first and second time<a name="line.32"></a>
<FONT color="green">033</FONT>     * derivative of the initial state vector, which can be handled by the<a name="line.33"></a>
<FONT color="green">034</FONT>     * underlying second order equations set.&lt;/p&gt;<a name="line.34"></a>
<FONT color="green">035</FONT>     *<a name="line.35"></a>
<FONT color="green">036</FONT>     * &lt;p&gt;One should be aware that the data is duplicated during the<a name="line.36"></a>
<FONT color="green">037</FONT>     * transformation process and that for each call to {@link<a name="line.37"></a>
<FONT color="green">038</FONT>     * #computeDerivatives computeDerivatives}, this wrapper does copy 4n<a name="line.38"></a>
<FONT color="green">039</FONT>     * scalars : 2n before the call to {@link<a name="line.39"></a>
<FONT color="green">040</FONT>     * SecondOrderDifferentialEquations#computeSecondDerivatives<a name="line.40"></a>
<FONT color="green">041</FONT>     * computeSecondDerivatives} in order to dispatch the y state vector<a name="line.41"></a>
<FONT color="green">042</FONT>     * into z and zDot, and 2n after the call to gather zDot and zDDot<a name="line.42"></a>
<FONT color="green">043</FONT>     * into yDot. Since the underlying problem by itself perhaps also<a name="line.43"></a>
<FONT color="green">044</FONT>     * needs to copy data and dispatch the arrays into domain objects,<a name="line.44"></a>
<FONT color="green">045</FONT>     * this has an impact on both memory and CPU usage. The only way to<a name="line.45"></a>
<FONT color="green">046</FONT>     * avoid this duplication is to perform the transformation at the<a name="line.46"></a>
<FONT color="green">047</FONT>     * problem level, i.e. to implement the problem as a first order one<a name="line.47"></a>
<FONT color="green">048</FONT>     * and then avoid using this class.&lt;/p&gt;<a name="line.48"></a>
<FONT color="green">049</FONT>     *<a name="line.49"></a>
<FONT color="green">050</FONT>     * @see FirstOrderIntegrator<a name="line.50"></a>
<FONT color="green">051</FONT>     * @see FirstOrderDifferentialEquations<a name="line.51"></a>
<FONT color="green">052</FONT>     * @see SecondOrderDifferentialEquations<a name="line.52"></a>
<FONT color="green">053</FONT>     * @version $Id: FirstOrderConverter.java 1416643 2012-12-03 19:37:14Z tn $<a name="line.53"></a>
<FONT color="green">054</FONT>     * @since 1.2<a name="line.54"></a>
<FONT color="green">055</FONT>     */<a name="line.55"></a>
<FONT color="green">056</FONT>    <a name="line.56"></a>
<FONT color="green">057</FONT>    public class FirstOrderConverter implements FirstOrderDifferentialEquations {<a name="line.57"></a>
<FONT color="green">058</FONT>    <a name="line.58"></a>
<FONT color="green">059</FONT>        /** Underlying second order equations set. */<a name="line.59"></a>
<FONT color="green">060</FONT>        private final SecondOrderDifferentialEquations equations;<a name="line.60"></a>
<FONT color="green">061</FONT>    <a name="line.61"></a>
<FONT color="green">062</FONT>        /** second order problem dimension. */<a name="line.62"></a>
<FONT color="green">063</FONT>        private final int dimension;<a name="line.63"></a>
<FONT color="green">064</FONT>    <a name="line.64"></a>
<FONT color="green">065</FONT>        /** state vector. */<a name="line.65"></a>
<FONT color="green">066</FONT>        private final double[] z;<a name="line.66"></a>
<FONT color="green">067</FONT>    <a name="line.67"></a>
<FONT color="green">068</FONT>        /** first time derivative of the state vector. */<a name="line.68"></a>
<FONT color="green">069</FONT>        private final double[] zDot;<a name="line.69"></a>
<FONT color="green">070</FONT>    <a name="line.70"></a>
<FONT color="green">071</FONT>        /** second time derivative of the state vector. */<a name="line.71"></a>
<FONT color="green">072</FONT>        private final double[] zDDot;<a name="line.72"></a>
<FONT color="green">073</FONT>    <a name="line.73"></a>
<FONT color="green">074</FONT>      /** Simple constructor.<a name="line.74"></a>
<FONT color="green">075</FONT>       * Build a converter around a second order equations set.<a name="line.75"></a>
<FONT color="green">076</FONT>       * @param equations second order equations set to convert<a name="line.76"></a>
<FONT color="green">077</FONT>       */<a name="line.77"></a>
<FONT color="green">078</FONT>      public FirstOrderConverter (final SecondOrderDifferentialEquations equations) {<a name="line.78"></a>
<FONT color="green">079</FONT>          this.equations = equations;<a name="line.79"></a>
<FONT color="green">080</FONT>          dimension      = equations.getDimension();<a name="line.80"></a>
<FONT color="green">081</FONT>          z              = new double[dimension];<a name="line.81"></a>
<FONT color="green">082</FONT>          zDot           = new double[dimension];<a name="line.82"></a>
<FONT color="green">083</FONT>          zDDot          = new double[dimension];<a name="line.83"></a>
<FONT color="green">084</FONT>      }<a name="line.84"></a>
<FONT color="green">085</FONT>    <a name="line.85"></a>
<FONT color="green">086</FONT>      /** Get the dimension of the problem.<a name="line.86"></a>
<FONT color="green">087</FONT>       * &lt;p&gt;The dimension of the first order problem is twice the<a name="line.87"></a>
<FONT color="green">088</FONT>       * dimension of the underlying second order problem.&lt;/p&gt;<a name="line.88"></a>
<FONT color="green">089</FONT>       * @return dimension of the problem<a name="line.89"></a>
<FONT color="green">090</FONT>       */<a name="line.90"></a>
<FONT color="green">091</FONT>      public int getDimension() {<a name="line.91"></a>
<FONT color="green">092</FONT>        return 2 * dimension;<a name="line.92"></a>
<FONT color="green">093</FONT>      }<a name="line.93"></a>
<FONT color="green">094</FONT>    <a name="line.94"></a>
<FONT color="green">095</FONT>      /** Get the current time derivative of the state vector.<a name="line.95"></a>
<FONT color="green">096</FONT>       * @param t current value of the independent &lt;I&gt;time&lt;/I&gt; variable<a name="line.96"></a>
<FONT color="green">097</FONT>       * @param y array containing the current value of the state vector<a name="line.97"></a>
<FONT color="green">098</FONT>       * @param yDot placeholder array where to put the time derivative of the state vector<a name="line.98"></a>
<FONT color="green">099</FONT>       */<a name="line.99"></a>
<FONT color="green">100</FONT>      public void computeDerivatives(final double t, final double[] y, final double[] yDot) {<a name="line.100"></a>
<FONT color="green">101</FONT>    <a name="line.101"></a>
<FONT color="green">102</FONT>        // split the state vector in two<a name="line.102"></a>
<FONT color="green">103</FONT>        System.arraycopy(y, 0,         z,    0, dimension);<a name="line.103"></a>
<FONT color="green">104</FONT>        System.arraycopy(y, dimension, zDot, 0, dimension);<a name="line.104"></a>
<FONT color="green">105</FONT>    <a name="line.105"></a>
<FONT color="green">106</FONT>        // apply the underlying equations set<a name="line.106"></a>
<FONT color="green">107</FONT>        equations.computeSecondDerivatives(t, z, zDot, zDDot);<a name="line.107"></a>
<FONT color="green">108</FONT>    <a name="line.108"></a>
<FONT color="green">109</FONT>        // build the result state derivative<a name="line.109"></a>
<FONT color="green">110</FONT>        System.arraycopy(zDot,  0, yDot, 0,         dimension);<a name="line.110"></a>
<FONT color="green">111</FONT>        System.arraycopy(zDDot, 0, yDot, dimension, dimension);<a name="line.111"></a>
<FONT color="green">112</FONT>    <a name="line.112"></a>
<FONT color="green">113</FONT>      }<a name="line.113"></a>
<FONT color="green">114</FONT>    <a name="line.114"></a>
<FONT color="green">115</FONT>    }<a name="line.115"></a>




























































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